The RNA modification database provides a comprehensive listing of posttranscriptionally modified nucleosides from all RNAs, and is maintained as an updated version of the initial printed report [Limbach,P.A., Crain,P.F. and McCloskey,J.A. (1994) Nucleic Acids Res., 22, 2183-2196], Information provided for each nucleoside includes: the RNA in which it occurs and phylogenetic distribution; name and symbol; Chemical number and index name; chemical structure; initial literature citations for structural characterization or occurrence, and for chemical synthesis, The data are available through the WWW and via anonymous ftp.